Free agency in Major League Baseball (MLB) concerns professional athletes whose contracts with a team have expired and who are therefore eligible to sign with another team. Specifics are governed by a collective bargaining agreement (CBA) between MLB and its players' labor union, the Major League Baseball Players Association (MLBPA). Before the mid-1970s, professional baseball players could effectively be bound, in perpetuity, to the team holding their contract via a "reserve clause", thus preventing them from becoming free agents.